1. Field of the Invention
The present invention relates to a motor control system for controlling a rotation of a stepping motor such as, e.g., a paper feed motor or the like in a printer.
2. Related Background Art
In general, a paper feed motor in a printer, etc. has hitherto involved the use of a stepping motor. In this type of printer, a high carrier accuracy of the recording paper has been required because of the attaining of a more sophisticated color reproducibility in color printing as well as of the fact that a high-accuracy and high-density printing operation could be obtained with an advancement of the printing technology.
For enhancing such a paper feed accuracy, the ratio of transmission from a paper feed motor to a carrier mechanism is reduced, and the paper feed quantity is controlled by employing a feedback technique, etc, thereby attaining sufficient accuracy. If the deceleration ratio is thus increased, however, the paper feed velocity decreases for the rotation of the motor. A large-sized motor has to be adopted to compensate for this decrease. As a result, there arise problems that the printer system increases both in size and in costs, and consumed the electric power increases.
Besides, during actuation of the stepping motor, if actuation does not occur from a self-starting range, the stepping motor can not be started up. Hence, the stepping motor is normally driven by effecting a ramp-up (acceleration control) from a low self-starting range. Typically, in the printer which uses a small-sized stepping motor, the least paper feed quantity required is matched with the minimum step angle of the stepping motor, thereby defining a deceleration ratio. The paper is fed in a through-area in combination with the ramp-up described above. At the same time, noises caused by the motor are reduced, and the paper feed control adapted to control the paper feed velocity is executed with a small amount of electric power consumed.
Generally, however, all the paper feed operations can not be necessarily controlled by the ramp-up operation. For instance, in a paper feed operation controlled by 3-step ramp-ups, in which paper feeding is less than three times the minimum step angle of the stepping motor, the paper feed comes to an end during these ramp-ups. As described herein, in the case of the small paper feed quantity, the paper has to be fed by rotating the stepping motor in the self-starting range. When operating the stepping motor in the self-starting range in this manner, however, the rotating power of the stepping motor increases. This causes vibrations and noises as well.
FIG. 2A is a diagram illustrating the vibrations caused when paper feeding is executed and then stopped after the actuation in the self-starting range described above. FIG. 2B is a diagram showing the vibrations caused when paper feeding is stopped after the actuation in a through-area. When the next operation command is inputted during the occurrence of vibrations after actuating the stepping motor, the next phase can not be surely magnetized because of an instability of a rotor state due to the vibrations. This results in the occurrence of an out-of-synchronism state. For preventing such an out-of-synchronism state, as disclosed in Japanese Patent Application Laid-Open No. 54-49026, the positioning phase continues to be magnetized by causing an electric current to flow thereto until the vibrations of the rotor are stopped. A positional relation between the rotor and a stator is thereby established, thus preventing the out-of-synchronism state. This method, however, presents the following problem. After operating the stepping motor, there is needed a waiting time until the vibrations of the rotor and the stator are stopped invariably for a period of several 10 ms through several 100 ms. Thus, the throughput is reduced, correspondingly.